This invention relates to a press apparatus for pressing dimensionally accurate pressed articles from a substantially powdered material.
Presses of this type generally serve to press powders or granulates of iron, ceramic constituents, or the like into pressed articles, e.g. gears or press-formed parts. The high specific pressing pressures, which may be as high as 30-100 kN/cm2 and more, require a very high stability of the press apparatus.
Schaidl et al., U.S. Pat. No. 4,482,307 (=DE 31 42 126) discloses a modular press, which comprises the actual press for applying the main pressing force and a press apparatus that can be inserted like an adapter into this actual press. This insertable press apparatus comprises a tool frame, which is coupled between the two platens of the press via an upper and a lower connecting device. This adapter-like press apparatus essentially consists of a frame of pull rods for guiding a plurality of plates, punch carriers and a die plate located between the connecting devices, which are likewise arranged or supported on the frame. In this arrangement, a base plate comprising the hydraulic devices for the relative movement of the individual plates, which are configured as punch carriers, is supported in the actual press by a mounting attachment. The additional plates are supported in the frame such that they are displaceable relative to the base plate. The die mounting plate is rigidly connected with the lower connecting device of the adapter via the frame and is arranged in the frame such that it is displaceable relative to the upper connecting device of the adapter. The individual punch carriers can be hydraulically moved relative to the base plate, such that they can be displaced between a charging position in which the lower die opening of the die mounting plate can be filled with a powder, and a final press position in which the powder is pressed into a pressed article by the press punches. The punches for pressing the powder are seated on the respective punch carriers. In the final press position, the individual punch carriers are supported against fixed stops. Both the piston/cylinder devices for hydraulically driving the individual punch carriers and the fixed stops are arranged in the outer peripheral region of the punch carriers, spaced a distance from the respective central openings of the individual punch carriers. The central openings in the individual punch carriers are configured in such a way that each of the punches seated on one of the punch carriers that is further away from the die mounting plate can be guided through the openings of the punch plates that are closer to the die mounting plate.
To improve the guidance of the punch carriers, Fleissner et al., EP 436,792 (=DE 40 00 423) proposes a press for producing dimensionally accurate pressed articles from a powdered material. This press has an upper and a lower press platen and a tool frame that can be inserted like an adapter into the press. This tool frame can be connected to the lower platen via a lower coupling plate and to the upper platen via an upper connecting piece. On a base plate of the tool frame, which is firmly supported in the press, a displaceably supported frame of pull rods is arranged. These pull rods rigidly connect the lower coupling plate wit a die mounting plate. Furthermore, punch carriers can be moved from the base plate into the charging and pressing positions by piston/cylinder drives. To improve guidance, this publication proposes that the punch carriers be shaped as cups, which are guided along cylindrical surfaces relative to the base plate. In this arrangement, the punch carriers are also supported against fixed stops in the final press position.
Both of these arrangements require careful adjustment of the individual punch carriers relative to one another and relative to the frame in order to prevent tilting or uneven pressing. A particular problem is the position of the fixed stops, which especially for the third punch carrier from the base plate engage underneath the outer rim of the punch carrier far away from the central opening. In the final press position, this has the result that the corresponding punch carriers are supported along the outside against a fixed stop, while the inside of the punches adjacent the through opening is acted upon by an opposite pressing force. This causes deflection of the punch carrier, which must be compensated by adjusting the pressing forces, which in practice requires a large number of individual trials. For high press cycles, regular readjustment is additionally required, e.g. to compensate the influences of fluctuating powder qualities.